1. Field of the Invention
The present invention relates to area management systems, and more specifically, to an area management system for a multicast service for allowing a plurality of wireless terminals to receive a flow transmitted from a wireless base station, in a wireless system for conducting voice or data communication, with control information sent from the wireless base station.
2. Description of the Related Art
With the proliferation of broadband, technological advances of routers and other apparatuses, the growing need of end users for receiving broadband streaming pictures and the like, and advances in producer-driven solutions, the multicast technology, which can broadcast data with a fewer communication resources than the unicast technology, has been attracting growing interest in the communication field. With the multicast technology, a router placed between a server and clients makes a required number of duplicates of one packet or one data stream and delivers the duplicates to a plurality of users simultaneously. In comparison with the unicast method, in which data is exchanged with a plurality of parties in a one-to-one relationship, the multicast technology can reduce the traffic volume on the network and can reduce the load on the server that delivers data.
In the wireless communication field, a communication technology for allowing a plurality of wireless terminals to receive one data stream has been studied to increase the efficiency of the wireless band and network. The conventional wireless communication system uses one-to-one unicast communication, in which a physical channel is assigned to each wireless terminal, and a wireless connection is established for communication. In one communication technology under study, one certain channel of the physical channels is specified as a multicast channel, and data having a multicast IP address is sent therethrough. This technology enables a plurality of wireless terminals to receive one data stream, and the wireless band can be used efficiently.
Generally, a wireless base station has one or more sectors. It is conceivable that the radio reception of a wireless terminal depends on the radio propagation environment in a sector where the wireless terminal is located. In unicast communication, in which one-to-one communication is conducted between the wireless terminal and the wireless base station, the data rate can be controlled in accordance with the radio environment of the wireless terminal, such as increasing the data rate of the transmission data when the radio reception (propagation state) of the wireless terminal is good and decreasing the data rate when the radio reception (propagation state) is bad. In multicast communication, however, data transmitted at a certain data rate on the multicast channel must be received, and some wireless terminals may not be able to receive the multicast data when the radio environment is too poor to receive the data at the data rate. Whether the data received by a wireless terminal can be decoded or not generally depends on the ratio of the magnitude of the received actual data to the magnitude of interference noise, for instance. The ratio of the magnitude of the actual data signal to the magnitude of the interference noise must be increased so that more wireless terminals can receive the multicast data at a certain data rate.
If a wireless terminal communication technology Code Division Multiple Access (CDMA) is used, for instance, the conventional unicast communication technology selects a sector of the best radio environment for communication, and all the radio waves sent from the other neighbor sectors become interference noise. In multicast communication, the same data is sent at the same timing (or substantially at the same timing) in a plurality of neighbor sectors by using the same frequency, and the wireless terminal receives and combines the data signals, so that the ratio of the intensity of the actual data to the intensity of interference noise can be increased. This technology is named soft-combine and is described in 3rd generation partnership project 2 (3GGP2) C.S0054, for instance.
With the method of sending the same data at the same timing in neighbor sectors and receiving and combining, by wireless terminals, the signals sent at the sectors, the ratio of actual data to interference noise increases, and more wireless terminals can receive multicast data, in comparison with the method of selecting a sector in a good radio environment for communication. The wireless base station incorporates a data transmission timing in control information and broadcasts the information to wireless terminals at regular intervals.